Crymsin Ost, a Human female strong in the Force, became a member of the Jedi Order as the Galactic Republic neared its end in its final years. She later fell to the dark side of the Force, joining the Believers, a Sith cult operating from the Cularin system. Around 21 BBY, amidst the Clone Wars, she journeyed to the Caarimoos system to lead a Believer operation. Their aim was to release a deadly virus on the planet of Caarimon, intending to decimate the Caarite species. However, a team of freelance agents intervened, thwarting her plans and preventing the virus's release.
Crymsin Ost was a Human female attuned to the Force who dedicated herself to the Jedi Order during the Galactic Republic's final years. Her training led her to become a Jedi Guardian, a Jedi specialization focused on combat. At some point, Ost's mental state deteriorated, and she embraced the dark side of the Force. Abandoning the Jedi, she aligned herself with the Believers, a Sith cult with its base in the Cularin system. She rose to prominence within the cult and, aided by the Ithorian Believer Force Adept Disch'l, constructed a lightsaber that emitted a pink blade.
Around 21 BBY, during the Clone Wars, the Believers hatched a scheme to wipe out the majority of the Caarites—a sentient species that operated the Metatheran Cartel trade organization—by unleashing a deadly virus on their homeworld, Caarimon. Ost was appointed to lead the operation, traveling to Caarimon aboard a transport carrying large quantities of the virus from a secret Believers laboratory located on the planet Genarius. Upon arriving in the Caarimoos system, Ost's transport docked with the research station Creautaa-V, which was in orbit around Caarimon. She then disembarked from the vessel with her strike team: Disch'l, the Believer Eph, and Melo Centris, a renowned assassin hired to assist the Believers. The Believers released a sample of the infection, killing all of the installation's Caarite crew, then off-loaded a tank of the virus and ferried it to the lowest level of the station. There, they filled some escape pods with the virus and prepared them for launch in the direction of the planet. They also rigged the pods with explosives, hoping to crash them into fault lines in the Desolation region of the world and cause a major cataclysm. Meanwhile, another group of Believers landed on Caarimon and rigged a homing beacon in the Desolation region, and Ost and her crew waited to receive a signal from the transmitter.
A group of freelance agents from the Cularin system, known as the "Heroes of Cularin," journeyed to Caarimon to investigate the Believer plot. After disabling the homing beacon in the Desolation, they boarded Creautaa-V and confronted Ost's strike team. Ost activated her lightsaber and attacked the operatives, while Disch'l used the Force to create an illusory version of the fallen Jedi as a distraction. Despite their efforts, Ost and the other Believers were ultimately defeated, and the agents prevented the virus from being released on the planet.
Crymsin Ost was mentally unstable and deeply committed to the Believers' ideology, readily embracing genocide to advance the cult's objectives. Like all Believers, she bore a tattoo on her right shoulder, depicting the Sith Fortress on Almas, with a broken lightsaber handle forming the base of the fortress's spire. Uniquely, Ost's tattoo was modified: a specific teeth-clicking pattern triggered fatal poison release from subdermal implants beneath the tattooed lightsaber handle, coloring each half of the blade red.
Ost was accustomed to fighting alongside an illusory duplicate, such as the one created by Disch'l during her battle with the Heroes of Cularin. She possessed Force abilities including sensing, telekinesis, healing, combat enhancement, and energy absorption. Furthermore, she had knowledge of the powers Battlemind, Force rage, Force stealth, and Hatred, and had training in martial arts.
Ost's weapon was a lightsaber, which emitted a bright pink blade tinged with red. The weapon's handle was constructed of black steel and was activated by an internal switch via the Force. She also carried a blaster pistol as a backup and wore casual clothing during the assault on Creautaa-V.
Crymsin Ost's sole canon appearance occurred in Belly of the Beaast, a roleplaying adventure crafted by Morrie Mullins in 2003, which was part of the Metatheran Caution trilogy within the Living Force campaign. In the adventure, players roleplay as the Heroes of Cularin, and Ost's Force power set varies with the players' experience tier. She only uses Drain Energy, Force Rage, and telekinesis, or martial arts against mid- or upper-tier players, and Hatred only against upper-tier players. Consequently, against lower-tier players, Disch'l must ignite her lightsaber, as she lacks telekinesis to activate its switch. Players can potentially kill Ost and loot her lightsaber. If captured, she attempts suicide by activating her tattoo implants.